A functional gene discovery in the Fas-mediated pathway to apoptosis by analysis of transiently expressed randomized hybrid-ribozyme libraries.

The sequence of much of the human genome is now available and the next goal is to identify functional genes and to clarify their roles. We have recently developed a novel system for isolation of genes in the Fas- and TNF-alpha-mediated pathways to apoptosis using poly(A)-connected hammerhead ribozyme libraries with randomized substrate-binding arms at both the 5' and 3' ends of ribozymes. The transcripts of these hybrid ribozymes have a poly(A) motif that can recruit RNA helicases and, thus, they can effectively attack target sites. In the previous studies, hybrid ribozymes were stably expressed. In order to save selection times, in this study we adopted transiently expressed hybrid ribozymes. In the case of Fas-mediated apoptosis, when we transiently introduced these hybrid-ribozyme libraries into Fas-expressing HeLa cells, we were able to isolate surviving clones that were resistant to or exhibited a delay in Fas-mediated apoptosis. We identified many pro-apoptotic genes and novel genes using this strategy with these transiently expressed hybrid-ribozyme libraries. In contrast, we identified significantly smaller numbers of candidate genes using conventional ribozyme libraries that were expressed transiently. Thus, when changes of a particular phenotype occur within a short period of time, our gene discovery system based on transiently expressed hybrid-ribozyme libraries should also be useful for the rapid identification of functional genes in the post-genome era.